1. Field of the Invention
The present invention relates generally to the clamps used to hold the lengthwise edges of a fabric, web, or sheet to be stretched in a tenter apparatus, and more specifically to those which use tenter pins to hold those edges.
2. Description of the Prior Art
Tenter apparatus and their associated pin plates are well known in the art. Standard pin plates consist& of a bed plate having rows of sharp pins protruding at a slight angle from a direction perpendicular to the bed plate and in the direction the fabric is to be stretched. The fabric is typically pressed onto these pins by means of a rotating brush.
In practice, a plurality of the bed plates are arranged to follow an endless conveyor track, or raceway, opposite a similar conveyor track. At the point where the fabric to be stretched on the tenter apparatus is introduced, the conveyor tracks are separated by a distance approximately equal to that of the width of the fabric. From that point, the conveyor tracks proceed parallel to one another for a predetermined distance, then diverge from one another by an amount equal to the degree of transverse stretching desired. The stretching may take place while the tenter apparatus is conveying the fabric through a heating zone. Longitudinal stretching may be accomplished at the same time by providing the endless conveyor tracks with means for separating adjacent bed plates on each track from one another while the tracks are diverging. In any event, after the fabric has been stretched in the transverse, and perhaps longitudinal, direction, the endless conveyor tracks again take on directions parallel to one another, although now more widely separated. At the end of the tenter apparatus, of course, the fabric, now stretched, is removed from the tenter pins.
Alternatively, the conveyor tracks may remain parallel to one another and separated by a constant amount for the entire length of the tentering apparatus. In such a situation, the tentering apparatus is used to prevent shrinkage while the tentered fabric is being conveyed through a heating, or other treatment, zone.
One serious difficulty with pin tentering is that the fabric tension load on the tenter apparatus is poorly distributed because it is carried only at those points where a pin penetrates the fabric. In addition, the edge of the fabric may suffer damage as the pin is removed after the fabric has been stretched, if the fabric remains under tension when this is being done.
The purpose of the present invention is to eliminate and overcome these serious difficulties in the prior art by providing a pin tenter clamp which clamps the fabric and maintains it under tension while the tenter pins are inserted and retracted therefrom, and which prevents the fabric from slipping off the tenter pins.